Cryostat



y 12, 4 w. B. COTTINGHAM ETAL 3,133,144

CRYOSTAT Filed Aug. 16, 1962 2 Sheets-Sheet l W. B. COTT/NGHAM J. E.KUNZLER -Mew ATTORNEY May 12, 1964 w. a. COTTINGHAM ETAL 3,133,144

CRYOS'I'A'I Filed Aug. 16, 1962 2 Sheets-Sheet 2 NGHAM INVENTORS: Z 2. 7B M 5 W A TTORNEV United States Patent O 3,133,144 CRYOSTAT William B.Cottingham, Hanover, and John E. Kunzler,

Pleasant Grove, N.J., assignors to Bell Telephone LaboratoriesIncorporated, New York, N.Y., a corporation of'New York Filed Aug. 16,1962, Ser. No. 217,319 6 Claims. (Cl. 17415) This invention relates tocryostats and, more particularly, to cryostats for refrigeratingsuperconducting electromagnets.

Considerable use has been made recently of the discovery that certainsuperconductors can be shaped into solenoids. Superconductive solenoidsare capable of producing extremely high magnetic fields and for thisreason are valuable laboratory tools for such purposes as plasma andatomic research. These solenoids tend, however, to be diflicult to workwith because they must normally be contained in a bath of liquefied gassuch as helium to maintain the extremely low temperatures that arenecessary for superconductivity. Liquid helium, with a boiling point ofabout 4 K., requires suchelaborate insulation that the test volumeWithin the solenoid, as well as the solenoid itself, is almostinaccessible.

It is therefore an object of this invention to make more accessible thetest volume within a supercooled solenoid.

It is another object of this invention to simplify the cryostatstructure that is necessary for supercooling a superconductive solenoid.

Another object of this invention is a cryostat-solenoid package that canbe easily attached to other cryostat-solenoid packages for the purposeof forming a uniform, intense magnetic field of any desired length.

It is a further object of this invention to supercool a superconductivesolenoid efiiciently.

These and other objects of our invention are attained in an illustrativeembodiment thereof which comprises an evacuated cylindrical annularencasement containing a superconductive solenoid to be refrigerated toapproximately 4 K. According to one feature of the invention, theencasement is divided into successive concentric annular chambers. Anouter annular chamber contains liquid nitrogen which surrounds andinsulates an annular chamber of liquid helium. The helium chambersurrounds a chamber containing the superconductive solenoid. Within thesolenoid is a chamber containing folded piping for transmittingevaporated helium gases from the helium chamber. A cylindrical shieldthermal-1y connected to the liquid nitrogen chamber insulates the heliumpiping from the inner wall of the encasement. After the helium gasescool the inner surface of the solenoid they are transmitted out of thecryostat by an annular exhaust pipe that coaxially surrounds the heliuminput pipe so that the input liquid helium is efliciently insulated.

According to another feature of the invention the encasement includes apair of annular end plates having a plurality of por-tholes for exposingheavy steel spacers on the solenoid. The spacers can be keyed to similarspacers of other cryostat-solenoid packages so that an extended magneticfield of any desired length can be attained. The v spacers separate thesolenoids, which are attracted by powerful magnetic forces, they alignthe solenoids, and they act as thermal conductors. A i I These and otherobjects and features of the invention will be more fully appreciatedfrom a considerationof the following detailed description, taken inconjunction with the accompanying drawing, in which,

3,133,144 Patented May 1 2, 1 964 Referring now to FIG. 1 there areshown three cryostat packages 10, 11, and 12 which are joinedtogether inaccordance with the invention. Cryostat 10 is shown partly in sectionand comprises an evacuated encasement 14 having annular end plates 15and 16. Contained within the encasement is a solenoid 17 which is madeof a material such as an alloy of 75% niobium and 25% zirconium byweight, which displays superconductive characteristics at temperaturesapproaching absolute zero. The purpose of the cryostat is to maintainsuch low temperatures while electrical current flows through thesolenoid. As is known, under these conditions, a large mag netic fieldcan be produced in the test volume .18 surrounded by the solenoid 1-7. i

With reference to both of the figures, cryostat package 10 has two inputterminals 19 and 28 for receiving liquid nitrogen and liquid helium.Liquid nitrogen, with a boiling point of about77 K., is introduced intoan annular chamber 22 through an input line 23 in terminal 19 and oninput line 24 in terminal 20. The nitrogen in chamber 22 and input line23 is insulated by vacuum spaces within encasement 14 and terminal :19;experience has shown that it is not necessary to seal the end of inputpipes 23 and 24 which are accordingly left open.

Liquid helium, with a boiling point of about 4 K., is introduced intoanother annular chamber 25 through an inputline 26 in terminal 19 and aninput line 27 in. terminal 20. Heliumchamber 25 coaxially surrounds thesuperconductive solenoid 17 and maintains it at an appropriatelylowtemperature. The solenoid 17 is'contained within an annular chamber29 which is segmeuted by a plurality of ribs 30. When solenoid 17 isenergized the resulting magnetic field exerts a powerful attractiveforce among the coils thereof which tends to force them together.. Theribs .30 counter this force and maintain the desired shape of thesolenoid.

The inner surface of solenoid17 is cooled by a pair of folded pipes 31and 32 that transmit evaporated helium gas from helium chamber 25. Thehelium input pipes 26 and-27 are sealed by safety valves 33 and 34,respectively, which prevent the cold evaporated helium gas from escapingto the atmosphere. .Atthis juncture it should be pointedout that thecryostatpackages 10, L1, and 12 are structurally symmetricalso that theright portion of FIG. 2, which is only partially shown in cross-section,is essentially the same asthe leftportion; The safety valves 33 and 34allow passage of helium gas only if it builds up to a dangerously high.pressure; otherwise the gas is allowed to pass into pipes 3 1 and 32.

Pipes 31 and 32 are contained within an annular chamber 36 which isenclosed 'by the solenoid '17. ..As.can be seen from FIG; 1, pipes 31'and 32- are folded in a serpentine shape and are interleaved tofor-manannular cylinder within chamber 36. We-have found that thisconstruction gives uniformrefrigeration ofthe solenoid and makes-maximumuse of the evaporatedfhelium. Because the pipes are well insulated, as.will he explained later, the helium remains at essentially 4 as itcirculates through chamber 36.

' likewise, gas from folded pipe 31 is exhausted through FIG. 1 is aperspective view, partly in section, of our invention; and I FIG. 2 isasection taken along lines 2-2 of FIG. 1.

a vent 40 via an annular exhaust pipe that surrounds and insulateshelium input line 27. Further insulation is provided bya nitrogen shieldjacket 41 which surrounds annular exhaust pipe 37. The shield jacket ismade of a thermally conductive material such as copper and is conneetedto nitrogen input line 23 by a thermal conductor 42. Shield jacket 41 istherefore maintained at approximately liquid nitrogen temperature, 77 K.A similar shield jacket is included in terminal 20. For the sake ofclarity, exhaust pipe 37 and its associated elements are not shown inFIG. 1.

The solenoid 17 is advantageously energized by. a plurality of leadwires 57 which are connected to a plurality of leads 58 that are printedupon helium input line 26. The evaporated helium gases flowing throughexhaust pipe 37 cool the printed circuit leads 58 and prevent normalresistance heat in the leads from deleteriously boiling away liquidhelium in helium chamber 25.

A nitrogen shield 45 is used to insulate folded pipes 31 and 32. inessentially the same manner as described above. Shield 45 is of copperand is connected by thermal conductors 43 and 44 to shield jacket 41 andto a similar shield jacket in terminal 20 to maintain it at liquidnitrogen temperatures. It should also be noted that annular thermalconductor 43 and cylindrical thermal conduetor 44 are also at the liquidnitrogen temperature and therefore insulate the solenoid. The testvolume 18 is defined by an inner cylindrical wall 55. It can beappreciated, pantie any from FIG. 1, that test volume 18 is readilyaccessible and that objects are easily admitted and removed therefrom.It is, of course, not usually necessary to refrigerate the test volume.

Attached at each end of the solenoid are three stainless steel spacers46 arranged 120 degrees apart. Each of the spacers can be exposed by aporthole 47 which is either vacuum sealed by a cover (not shown) orclamped in a vacuum-tight relationship to other cryostat packages asshown in FIG. 1. By attaching two or more cryostat packages in thismanner a magnetic field of any desired length can be attained. However,the extraordinarily large attractive forces produced by the adjacentsolenoids would normally collapse them; the steel spacers 46 give sufficient ire-enforcement to prevent such collapse. Further, the spacers actas thermal conductors and thereby equalize the temperatures of adjacentsolenoids.

The spacers 46 on one end of each solenoid contain a key projection 49while the spacers on the other end contain a keyhole 50 adapted toreceive such a projection. When the three key projections of onesolenoid are fitted into the three keyholes [of an adjacent solenoid,the two solenoids are accurately aligned, This is an importantconsideration because if two adjacent solenoids are slightly misalignedtheir large magnetic fields will produce a torque that may actuallyrotate one solenoid around the other. To insure further their accuratealignment, each cryostat package is mounted on a platform 52, which inturn is mounted by wheels 53 on a common track 54. The desired number ofcryostat packages can then be placed on the track and rolled into anaccurate position with a minimum of alignment problems.

In summary, it can be appreciated that an important advantage of ourdevice is that it combines accessibility of the solenoid and thesolenoids test volume with eflicient cooling. Further, it is quiteflexible in that any desired number of packages can be combined. Thedevice shown was built to produce rflux densities of up to 100kilogauss. Each package is approximately 20 inches long and has aninside diameter of 7 inches with the other components beingsubstantially drawn to scale. It is to be understood, however, that thedisclosed embodiment is only illustrative of our invention. Variousother forms can be made by one skilled in the art without departing fromthe spirit and scope of the invention.

What is claimed is: 1. In combination: an evacuated cylindrical casinghaving a pair of-annular end plates; 7 said casing coaxially surroundinga first annular chamber adapted for containing liquid nitrogen; saidfirst annular chamber coaxiallysurrounding a sec- 0nd annular chamberadapted for containing liquid helium;

said second annular chamber adapted for coaxially surrounding a solenoidof superconducting material;

said casing having a cylindrical inner wall defining a central aperture;

a folded pipe which is constructed to define a hollow cylinder beinglocated between said solenoid and said inner wall;

said pipe being connected to said second chamber and being adapted totransmit evaporated helium therefrom;

said solenoid coaxially surrounding and being closely adjacent to saidfolded pipe;

a plurality of thermal conductors connected to each end of saidsolenoid;

and means in said end plates forexposing said thermal conductors.

2. A cryostat for supercooling a superconductive solenoid comprising:

a cylindrical encasement containing a plurality of concentriccylindrical chambers;

an input terminal at each end of said encasement;

a liquid nitrogen input pipe and a liquid helium input pipe in each ofsaid input terminals;

said nitrogen input pipe comprising means for transmitting liquidnitrogen to a first cylindrical chamber;

said helium input pipe comprising means for transmitting liquid heliumto a second cylindrical chamber within the first chamber;

a superconductive soienoid being contained in a third cylindricalchamber within the second chamber;

a pair of hollow pipes being contained in a fourth cylindrical chamberwithin the third chamber;

a cylinder of thermally conductive material which is connected to saidfirst chamber forming the inner wall of said fourth chamber therebythermally insulating said pair of pipes;

one end of each of said pipes being connected to an opposite end of saidsecond chamber and adapted for receiving evaporated helium gases and theother end of each of said pipes being connected respective ly to aseparate annular exhaust pipe; each of the annular exhaust pipescoaxially surrounding one of the liquid helium input pipes, therebythermally insulating the input pipes;

a plurality of steel spacers on each end of said third chamber;

the spacers on one end containing key projections and the spacers on theother end containing keyholes;

and a plurality of portholes in said encasement for exposing saidspacers.

3. The cryostat of claim 2 further comprising:

means for energizing said superconductive solenoid comprising printedcircuit leads printed on the exterior of said helium input pipes, saidleads being surrounded by said annular exhaust pipe, wherebysubstantially all resistance heat generated in the leads is dissipatedby helium gases flowing through the exhaust pipe.

4. A cryostat comprising:

an evacuated encasement having a cylindrical outer wall, a cylindricalinner wall and a pair of end plates;

said encasement containing first, second, third and fourth concentricannular chambers, the first chamber surrounding the second chamber, thesecond chamber surrounding the third chamber, and the third chambersurrounding the fourth chamber;

the first annular chamber being adapted to contain a first liquefiedgas; a

the second annular chamber being adapted to contain a second liquefiedgas having a lower boiling point than the first gas;

the third chamber containing a solenoid;

the fourth chamber containing piping which has an open end communicatingwith the second chamber and being adapted to transmit evaporated gasfrom the second chamber, thereby refrigerating the fourth chamber.

5. A device for producing an extended magnetic field of high intensitycomprising:

a plurality of encasements each having a cylindrical outer wall and acylindrical inner, wall connected by a pair of end plates;

two input terminals extending into opposite ends of the outer wall ofeach encasement;

each input terminal comprising a helium input pipe and nitrogen inputpipe;

each of the encasements containing a separate first annular chamberwhich is connected at opposite ends to a nitrogen input pipe;

each of said first annular chambers coaxially surrounding a separatesecond annular chamber which is con nected at opposite ends to aseparate helium input p p said nitrogen input pipes and said heliuminput pipes each respectively comprising means for transmitting liquidnitrogen to one of said first chambers and liquid helium into one ofsaid second chambers;

each of said second chambers coaxially surrounding a separate thirdannular chamber which is segmented into a. plurality of annularsub-chambers;

each of said sub-chambers containing a plurality of circular windings ofa wire made of superconductive material; 1

each of said third chambers coaxially surrounding a separate fourthchamber which contains two serpentine folded pipes;

said pipes each being connected to said second chamber and being adaptedto transmit evaporated helium therefrom;

each of said fourth chambers coaxially surrounding a separate fifthannular chamber which is defined by said fourth chamber and thecylindrical inner wall of the respective encasement;

each of said fifth chambers containing a cylindrical wall of thermallyconductive material which is thermally connected to said first chamber;

a plurality of spacers on each end of each of said third chambers;

the spacers on one end of each of the third chambers having keyprojections and the remaining spacers having key holes for receivingsaid projections;

and a plurality of portholes in each of said end plates for exposingsaid spacers;

the spacers of each of said third chambers being keyed to spacers ofother third chambers;

and the volume within the inner walls of all of said encasements forminga test volume for containing magnetic fields generated by saidsuperconductive windings. 6. A device for producing a high intensitymagnetic field comprising:

an encasement having a cylindrical outer wall and a v cylindrical innerwall being connected by annular end plates;

two input terminals extending into opposite ends of said outer wall;

each input terminal comprising a helium input pipe and a nitrogen inputpipe;

a first annular chamber Within said encasement being connected atopposite ends to a nitrogen input pipe;

said first annular chamber coaxially surrounding a second annularchamber which is connected at opposite ends to said helium input pipe;

said nitrogen input pipe and said helium input pipe respectivelycomprising means for transmitting liquid nitrogen to said first chamberand said helium to said second chamber;

said second chamber coaxially surrounding a third annular chamber whichis segmented into a plurality of annular sub-chambers;

each of said sub-chambers containing a plurality of circular windings ofa wire made of superconductive material;

said third chamber coaxially surrounding a fourth chamber which containstwo serpentine folded pipes which are interleaved with respect to eachother;

an annular exhaust pipe coaxially surrounding each of said helium inputpipes;

said folded pipes each being connected at one end to said second chamberand at the other end to opposite annular exhaust pipes and further beingadapted to transmit evaporated helium from said second chamber to one ofsaid exhaust pipes;

said fourth chamber coaxially surrounding a fifth annular chamber whichis defined by said fourth chamher and a cylindrical inner wall of theencasement;

said fifth chamber containing a cylindrical Wall of thermally conductivematerial which is thermally connected to said first chamber, all of saidfive chambers being separated from each other and from said outer wallby an annular vacuum space;

a plurality of spacers on each end of said third chamber;

the spacers on one end of the third chamber having key projections, theremaining spacers having key holes for receiving key projections;

and a plurality of portholes in each of said endplates for exposing saidspacers.

References Cited in the file of this patent UNITED STATES PATENTSBurstein Dec. 10, 1957

4. A CRYOSTAT COMPRISING: AN EVACUATED ENCASEMENT HAVING A CYLINDRICALOUTER WALL, A CYLINDRICAL INNER WALL AND A PAIR OF END PLATES; SAIDENCASEMENT CONTAINING FIRST, SECOND, THRID AND FOURTH CONCENTRIC ANNULARCHAMBERS, THE FIRST CHAMBER SURROUNDING THE SECOND CHAMBER, THE SECONDCHAMBER SURROUNDING THE THIRD CHAMBER, AND THE THIRD CHAMBER SURROUNDINGTHE FOURTH CHAMBER; THE FIRST ANNULAR CHAMBER BEING ADAPTED TO CONTAIN AFIRST LIQUEFIED GAS; THE SECOND ANNULAR CHAMBER BEING ADAPTED TO CONTAINA SECOND LIQUEFIED GAS HAVING A LOWER BOILING POINT THAN THE FIRST GAS;THE THIRD CHAMBER CONTAINING A SOLENOID; THE FOURTH CHAMBER CONTAININGPIPING WHICH HAS AN OPEN END COMMUNICATING WITH THE SECOND CHAMBER ANDBEING ADAPTED TO TRANSMIT EVAPORATED GAS FROM THE SECOND CHAMBER,THEREBY REFRIGERATING THE FOURTH CHAMBER.